1. Field of the Invention
The present invention relates to an image data processor which processes image data so that a picture image including image data at intermediate gradient can be telegraph-transmitted at a high speed.
2. Description of the Prior Art
Conventionally, as a method of telegraph-transmitting an image at intermediate gradient in facsimile apparatuses, a method of encoding the intermediate gradient for every pixel, an intermediate gradient telegraph-transmitting method using a dither method, and the like are known.
The former method of encoding the intermediate gradient for every pixel has drawbacks such as that it is not compatible with the telegraph-transmitting method for a binary signal which is generally used and that it takes a longer time for telegraph-transmission as the number of slice levels of the intermediate gradient is increased.
On the other hand, the latter telegraph-transmission by the dither method has drawbacks such as that resolution is equally bad and the quality of an image received is also bad, and that if an encoding method such as MH (Modified Huffman) or MR (Modified Read) or the like specified in the recommendation T4 by the CCITT (International Telegraph and Telephone Consultative Committee) which was determined on the basis of the statistical nature of a picture image is used as it is, the efficiency in transmission is extremely bad and high speed telegraph-transmission is difficult.